feat(mcp): add runner config sync

[doyled-it]

Summary

Add a command palette workflow for comparing configured MCP servers across runners, and automatically sync missing Claude/Codex MCP server definitions before the New Session dialog loads its runner-specific MCP list.

Changes

• Added an MCP sync planner for Claude and Codex configs, with OpenCode shown as unsupported for sync.
• Added a Sync MCP Servers command palette action and overlay showing inventory, an all-missing sync action, individual sync actions, and write previews.
• Auto-sync missing Claude/Codex server definitions when opening New Session from either the command palette or the n shortcut, so runner toggles see the same configured server set immediately.
• Wired README guidance, help overlay copy, and tests for parsing, diffing, preservation, single-action confirmation, all-missing confirmation, automatic command-palette sync, and automatic shortcut sync.

Testing

• cargo test --all-features (792 passed, 3 ignored)
• cargo test --all-features test_new_session_ (command-palette and shortcut New Session regression coverage)
• prek run --all-files (cargo fmt, cargo clippy, cargo test, and release build all passed)
• Manually exercised the affected flows: launched target/release/agent-view, opened Ctrl+K, selected Sync MCP Servers, verified the inventory/preview overlay, and exited without confirming a write.

Screenshots / Recordings

Not attached. Manual smoke coverage verified the terminal overlay rendered the inventory and preview.

Version Label

version:minor

Related Issues

Closes: #67

Checklist

• Commits follow Conventional Commits
• Code follows the layering rules in CONTRIBUTING.md (no UI imports in core/, no state mutation in ui/)
• New code is covered by tests where practical
• Documentation (README, in-repo docs, help overlay) updated if behavior changed
• A version:* label is applied (or this change intentionally ships without a release)